February 05, 2012

Six Lesser-Known Climate Facts

Climate change seems to have taken a back seat lately both in policy debates and business strategies. But this is generally not the case in the research community, where rigorous analyses of climate change mitigation proposals are being published regularly. Herewith are six lesser-known recent findings that help separate the promise from the hype.

About 18% of global warming is caused by black carbon, which is not a greenhouse gas. A result of incomplete combustion of fossil fuels and solid biofuels, black carbon stays in the atmosphere for just days to weeks and works by absorbing light and radiating out heat. The heated air molecules last longer and can move long distances. Black carbon also reduces the earth’s albedo (reflectivity) when deposited on snow and ice, which further increases warming. Black carbon reduction could emerge as a major climate change mitigation technique with significant health benefits.

Among greenhouse gases, methane emissions present a mitigation opportunity similar in scale to black carbon. The energy industry (oil and gas production, gas transmission, and coal mining) and waste handling (municipal waste, wastewater, and livestock manure) are two large contributors, both of which have readily available technologies to control emissions. Lower methane levels also help increase crop yields.

When dead trees on forest floors decompose, they release previously sequestered carbon back into the atmosphere in about 10 years. Slowing down this decomposition by burying or storing the fallen logs in anaerobic conditions could potentially sequester large amounts of additional carbon for hundreds of years at a relatively low cost. The mitigation potential is larger than that of black carbon or methane. There are risks that would have to be managed, such as nutrient lockup, habitat loss, disturbance to forest floors and soils, and the need for some road construction.

Can afforestation (planted forests) sequester enough carbon to seriously mitigate climate change? Since afforestation reduces surface albedo and increases absorption of solar radiation, the net benefits are generally low and even negative in some cases. A simulation study has shown that afforestation is much more effective in the tropics – owing to the higher evapotranspiration – than in temperate and boreal regions. There is at least one interesting proposal out there to “end” global warming through irrigated afforestation of subtropical deserts.

Can white roofs be part of the solution to tackle climate change? White roofs do reduce the energy needed to cool buildings in the summer, but could increase energy use for heating in the winter – which might more than offset the savings. Moreover, while white roofs do cool urban surfaces – counteracting the urban heat island effect – they reduce cloudiness slightly and allow more sunlight to reach the earth’s surface. And the light reflected from the roofs cause some additional warming through absorption by black carbon. The likely net effect is additional warming of the earth – except perhaps in areas with low winter heating needs and in conjunction with black carbon reduction.

Does composting always produce lower greenhouse gas emissions than landfilling organic waste? Composting does require energy for turning the piles in order to minimize methane emissions, but finished compost could replace synthetic fertilizer. On the other hand, landfills do generate methane, but increasingly much of that is collected and used as fuel or flared. Plus, landfills provide carbon storage through the undecomposed portion of the waste. One recent study found that windrow composting of yard waste produces significantly higher net emissions compared to using that waste as alternative daily cover in landfills equipped with gas collection.

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Kumar Venkat is president and chief technologist at CleanMetrics Corp., a provider of analytical solutions for the sustainable economy.